Objective: To better understand morbidity and mortality in patients with a low left ventricular ejection fraction (LVEF) undergoing aortic root replacement. Methods: All patients who underwent aortic root replacement at our institution between 2005 and 2013 (n = 595) were retrospectively reviewed and included in the study. The primary outcome was mortality. Secondary outcomes were in-hospital mortality and perioperative morbidity. Restricted cubic spline analysis showed a relatively linear inverse relationship between LVEF and the hazard ratio for mortality in patients with an LVEF <50% with no unique cutoff. Therefore, LVEF was treated as a continuous variable. Patients were divided into 3 groups (LVEF <40%, LVEF 40%-49%, and LVEF ≥50%) in order to illustrate the impact of LVEF on mortality. Results: LVEF <40% patients had greater in-hospital mortality (14.0% vs 5.0% vs 1.0%, P < .001) and longer median hospital and intensive care unit stays (10.5 vs 8 vs 6 days, P < .001 and 4 vs 2 vs 2 days, P < .001) than patients with LVEF 40% to 49% or greater than 50%, respectively. Patients with LVEF <40% had more reoperations for bleeding (18% vs 5.0% vs 5.8%, P = .004), postoperative respiratory failure (16% vs 6.7% vs 4.9%, P = .008), and need for mechanical circulatory support (8.0% vs 5.0% vs 1.4%, P = .005). Using multivariable Cox proportional hazards analysis, we found that reduced LVEF, age, previous, cardiac surgery, and type A dissection were independent predictors of mortality. Conclusions: Reduced LVEF negatively impacts mortality as well as in-hospital death and perioperative morbidity after aortic root replacement. Careful patient selection and risk discussion are vital in this high-risk population.